Hippocrates first observed and wrote about negative reactions to cow’s milk around 370 BC, and since then the prevalence, awareness and understanding has increased. Milk allergy is defined, as hypersensitivity to cow's milk protein by a mechanism involving the immune system. An adverse reaction to milk that does not involve an immune mechanism is defined as Milk Intolerance.

Milk is one of the most common food allergens in children. Studies in several countries around the world show a prevalence of milk allergy in children in the first year of life of around 2% to 5%. Many children lose their hypersensitivity to milk by age 3, but some children remain allergic for a lifetime.

Cow's milk contains at least 20 protein components that may provoke an antibody response. The milk proteins, casein and whey are to blame. Caseins give milk its "milky" appearance and the whey makes up the remainder of the milk substance. Most commercial sources of whey are contaminated with casein proteins, and vice versa, so it can be hard to find truly “milk-free” foods.

As with most allergies, avoidance is key. Make sure to read all labels for foods, cosmetics, medicines, creams and ointments that may contain any type or amount of cow’s milk. A history of allergic reactions shortly after exposure to cow’s milk might suggest an allergy. However, this should be confirmed with a skin prick test or RAST. Talk to your doctor about a complete diagnosis.